In known UHF receivers, a volume control is provided which varies the volume in dependence upon the field strength of the received signal. In the absence of a signal received at the antenna or in the presence of a very weak signal, the volume is substantially decreased so that the noise which would otherwise be generated is suppressed. For car radios, it is particularly desirable that the volume control be effected very rapidly following a change in field strength. The line connecting the output terminal of the IF section which furnishes the field strength signal to the control input of the volume control circuit thus has a very small time constant. The field strength signal at the corresponding output terminal of the IF section is first applied to an amplifier. An RC circuit is connected to the output of the amplifier, the time constant of the RC circuit determining the time constant of the connecting line. The control input of the volume control circuit is connected to the common point of the resistor and the capacitor of the RC circuit.
If now two high frequency carrier oscillations are received at the antenna of the UHF receiver which originate from the same point but which, due to different transit times, have different modulation content, a so-called multipath reception results. This multipath reception causes, among other things, an amplitude modulation of the received signals which means that the signal is both amplitude and frequency modulated. As a result, distortion of a greater or lesser degree will occur.
These low frequency amplitude modulations also affect the field strength signal. This in turn causes a modulation of the volume control signal which again causes distortion.